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--- blog:articles:orbital_shenanigans [2019/02/16 01:03] – created Phil Ide
+++ blog:articles:general:orbital_shenanigans [2019/03/06 10:37] – Phil Ide
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 ====== Orbital Shenanigans ======
+{{blog:articles:mars_map2.png|MOLA map of Mars coloured by elevation}}\\
 Sometimes when you do some research – actually, quite often – you find out some really interesting stuff and end up changing your mind. In my story, I had some people on the ground on Mars, and wanted a spacecraft in a geostationary orbit above them to give them communications between them at all times. Just for info, when talking about geostationary orbits, the accepted term for Mars is aerostationary. I’ll use geostationary and geosynchronous because it’s my blog and although the aero prefix is accepted, it isn’t mandatory.
+=== ===
 Since I’ve written a program that can calculate orbits around Mars (see the download section), figuring out the orbital parameters is easy enough for me, but I decided to check my results against published scientific papers. I like to be thorough in my research. This resulted in a delightful piece of serendipity, which I’ll talk about in a moment, and turned up some fascinating facts about these peculiar types of orbit that I’d never heard of.
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 Unfortunately, because of the wild variance in the Martian gravity field, maintaining station in a geostationary orbit around Mars turns out to be very difficult. It is simply too easy to begin sliding off-station. It would just be too much effort.
-So, back to the drawing board. Let’s tackle this another way. Another orbit, what you might call a ‘regular’ orbit, doesn’t have this problem. At least, not so much. One suggestion was to use a lower orbit at an elevation of 5,000km. Consider that at the geostationary orbit (13,634km), the satellite can see 30 degrees of the planet either side of the point it is above. That’s a 60 degree spread. At 5,000km, this reduces, but not by too much. This is important, so hang on to that information.
+So, back to the drawing board. Let’s tackle this another way. Another orbit, what you might call a ‘regular’ orbit, doesn’t have this problem. At least, not so much. One suggestion was to use a lower orbit at an elevation of 5,000km. Consider that at the geostationary orbit (17,215km), the satellite can see 30 degrees of the planet either side of the point it is above. That’s a 60 degree spread. At 5,000km, this reduces, but not by too much. This is important, so hang on to that information.
 A 5,000km orbit has a period of approx 0.26 days (that’s Earth days, not Martian ones, which are about half an hour longer). Using my orbital calculator, I finessed the orbit down to 4,781.361km. That gives it an orbital period of 6hrs 9mins and 53secs. If you do the sums in your head, you’ll see that four orbits come to approximately 24hrs 39 mins 35 secs – the same as a Martian day. So now we have exactly four orbits per day.
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 So, yeah. I went with it.
+~~socialite~~
+~~DISCUSSION~~